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use ::darling::FromDeriveInput;
use quote::quote;
use syn::Token;
mod kw {
syn::custom_keyword!(state);
}
struct AggrFunctionStateExpr(syn::Expr);
impl syn::parse::Parse for AggrFunctionStateExpr {
fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
input.parse::<kw::state>()?;
input.parse::<Token![=]>()?;
Ok(Self(input.parse()?))
}
}
#[derive(FromDeriveInput, Debug)]
#[darling(forward_attrs(aggr_function))]
pub struct AggrFunctionOpts {
ident: syn::Ident,
generics: syn::Generics,
attrs: Vec<syn::Attribute>,
}
impl AggrFunctionOpts {
pub fn generate_tokens(self) -> proc_macro2::TokenStream {
let state_expr = self
.attrs
.first()
.expect("Expect #[aggr_function] attribute")
.parse_args::<AggrFunctionStateExpr>()
.expect("Expect syntax to be #[aggr_function(state = expr)]")
.0;
let ident = &self.ident;
let name = ident.to_string();
let (impl_generics, ty_generics, where_clause) = self.generics.split_for_impl();
quote! {
impl #impl_generics crate::AggrFunction for #ident #ty_generics #where_clause {
#[inline]
fn name(&self) -> &'static str {
#name
}
#[inline]
fn create_state(&self) -> Box<dyn crate::AggrFunctionState> {
Box::new(#state_expr)
}
}
}
}
}